Researchers compared current temperatures with previous record highs from weather stations throughout Northern Europe, including three stations inside the Arctic Circle.

For each year in the historical record, scientists isolated the hottest three days of the year. These snapshots showed the planet is getting hotter over time. The data also showed this summer's heat wave is unprecedented.

"We found that for the weather station in the far north, in the Arctic Circle, the current heat wave is just extraordinary -- unprecedented in the historical record," Geert Jan van Oldenborgh, researcher at the Royal Netherlands Meteorological Institute, said in a news release.

Among the stations in the far north of Europe, scientists were unable to establish a trend or quantify the impact of global warming on this summer's heat, due to the high variability of Arctic summer temperatures.

"But for the three stations further south -- in the Netherlands, Denmark and Ireland -- the historical record does allow us to make a calculation, and it shows that climate change has generally increased the odds of the current heat wave more than twofold," van Oldenborgh said.

Scientists say the findings are preliminary and that more analysis is necessary to confirm the unprecedented nature of this summer's heat -- more detailed work that can't happen until after summer has ended. But researchers argue their work shows longer, hotter heat waves are to be expected moving forward.

"This is something that society can and should prepare for -- but equally there is no doubt that we can and should constrain the increasing likelihood of all kinds of extreme weather events by restricting greenhouse gas emissions as sharply as possible," said Friederike Otto, director of the Environmental Change Institute at Oxford University.

Researchers published their analysis of this summer's unprecedented heat online this week.

Previous studies have shown heatwaves on land and at sea are likely to get hotter, last longer and happen more frequently as atmospheric CO2 concentrations continue to rise. Heat waves could even make some parts of the planet uninhabitable.